Diode-lasers provide a most efficient and compact means of light generation and are attractive as light-sources in many applications, particularly those in which light is required only in a limited range of wavelengths. Such applications include, for example, medical applications such as photodynamic therapy and depilation; machining, welding, and heat treating using light; providing pump-light-sources for solid state lasers; and simply providing illumination.
Diode-laser-light-sources are frequently in the form of a "bar" which includes a plurality of individual lasers on a single semiconductor substrate. The lasers emit from the edge of the bar in a direction perpendicular to the length of the bar. Where one bar is insufficient to provide a desired power or brightness, an array of bars is used, one stacked above the other in a direction perpendicular to the emission-direction. Such an arrangement is usually referred to as a stacked-bar array, or a two dimensional array of emitters.
One relatively simple way of mounting such a stack of diode-laser bars is disclosed in U.S. Pat. No. 5,040,187. Here, in what may be described as a back-plane cooling arrangement, the diode-laser bars are mounted in metalized grooves in a common heat-sink of conductive ceramic material such as beryllia or alumina. In more elaborate arrangements each diode-laser bar is provided with an individual cooler and mechanical arrangements are provided for holding the bars and coolers in a unified array. In all such arrangements, the closer the bars are stacked, i.e., the more compact the output-aperture of the array, the brighter the array will be. Where the closely stacked bars are operated at high power or rapid pulse rates, however, problems are often encountered in removing heat generated during operation of the bars.
One prior-art solution to these problems has been to construct diode-laser bar arrays in which the diode-laser bars are separated horizontally as well as vertically. Such arrays are disclosed, for example, in German patent DE 2,153,969, and in Japanese patent JP 4,426,789. The disclosed arrays include a heat-sink having a stepped mounting surface with a diode-laser bar mounted on each step. Vertical spacing is comparable or even closer than in the case of arrays in which diode-laser bars are only vertically separated, while the horizontal spacing provides greater physical separation which facilitates cooling. The stepped mounting surface of the heat-sink, however, can be expensive to fabricate and also creates difficulty in using fluid-cooling arrangements, in particular microchannel-cooler arrangements, for the surfaces or steps on which the diode-laser bars are mounted. There is a need for a diode-laser-light-source in which diode-laser bars can be relatively widely spaced while still being effectively cooled and while still delivering light from a compact output-aperture.